Hydroquinone process

ABSTRACT

Hydroquinone is produced from the alkali metal salts of 2,5dichloroterephthalic acid by heating the salt at an elevated temperature in the presence of a limited amount of water.

[ 1 Sept. 18, 1973 HYDROQUINONE PROCESS [75] lnventor: Shigeto Suzuki, San Francisco, Calif.

[73] Assignee: Chevron Research Company, San

Francisco, Calif.

[22] Filed: Feb. 13, 1970 [21] Appl. No.: 11,309

[52] US. Cl. 260/621 R, 260/629, 260/650 R,

260/524 R [51] Int. Cl. C07c 29/00 [58] Field of Search 260/621 R, 629

[56] References Cited UNITED STATES PATENTS 1,737,842 12/1929 Hale et al 2601621 R 3,089,905 5/1963 Wygant 260/621 R 2,852,567 9/1958 Barnard et al. 260/621 R 12/1955 Pearlman 260/621 R X 12/1955 Kaeding et al. 260/621 R OTHER PUBLICATIONS Moller, Chem. of Org. Comp, 3rd edition, pp. 492-493, 1965 QD2S3.N65. Moller, lbid. p. 602.

Primary Examiner[.eon Zitver Assistant Examiner-Norman Morgenstern Att0rneyJ ohn Stoner, Jr., 0. F. Magdeburger, D. L. Hagmann and J. A. Buchanan, Jr.

[57] ABSTRACT Hydroquinone is produced from the alkali metal salts of 2,5-dichloroterephthalic acid by heating the salt at an elevated temperature in the presence of a limited amount of water.

9 Claims, No Drawings HYDROQUINONE PROCESS FIELD OF THE INVENTION This invention relates to a novel process for the production of hydroquinone, particularly from alkali metal salts of 2,5-dichloroterephthalic acid.

BACKGROUND OF THE INVENTION Hydroquinone is a well-known article of commerce. Conventional methods for its production include the reduction of quinone and the catalyzed cyclotrimerization of acetylene in the presence of carbon monoxide.

THE INVENTION It has now been found that hydroquinone can be prepared by heating a mixture of an alkali metal salt of 2,5- dichloroterephthalic acid, alkali metal hydroxide and water at a temperature in the range from about 150C. to 250C., preferably l90C. to 210C. for a period in the range from about 0.2 to 2 hours, and acidifying the resulting reaction product mixture. Preferably the reaction is promoted by the presence of a copper catalyst in the reaction mixture. Surprisingly, the presence of water in the reaction mixture does not adversely affect the reaction provided that the relative amount added is not toogreat. It appears on a molecular basis that the amount of water in the reaction mixture should not materially exceed the amount of the base and that the presence of a large relative amount of water operates detrimentally by reducing the basic strength of the hydroxide in the reaction mixture. For each mol of the salt, the reaction mixture should contain an amount of the hydroxide in the range from about 4 to mols, preferably 6-14 mols. Although the amount of water which can be tolerated in the instant process is small, nevertheless, it is sufficient to alleviate the aforementioned problems incidental to the ordinary fusion reaction system.

The production of hydroquinone by the present process is surprising in view of the art. U. S. Pat. No.

2,439,237 discloses that the treatment of polyhalosubstituted phthalic acid with a base yields polyhalobenzoic acid or polyhalobenzene. Apparently, in view of the present discovery, the geometric relationship of the carboxyl groups of a halo-substituted benzene dicarboxylate salt or acid drastically alters the course of and the products from displacements on aromatic carbon atoms. The products obtained from halosubstitutedphthalates (ortho carboxyl relationship) are different from those obtained from halo-substituted terephthalates (para carboxyl relationship). The former yield halo-substituted benzoic acid and/orhalosubstituted benzene, whereas the latter yields hydroquinone.

A'further conflicting factor in the present displace ment reactions on aromatic carbon in addition to the aforementioned geometric effect is associated with the pH'of the reaction medium. Apparently pH plays an important role in displacements on aromatic carbon atoms of functional groups. U. S. Pat. No. 3,4l3,341= discloses that in halogen displacements on polyfunctional substituted aromatic compounds effected at a pH below 7 halogen is displaced by hydroxyl and, where present, carboxyl groups are retained. The production' of hydroquinone as in the present process is consequently an unexpected albeit very useful result.

Hydroquinone is a well known article of commerce. 2,5-dichloroterephthalic acid on the other hand, while not of particular commercial importance, is readily available from the corresponding dichloro-para-xylene by conventional oxidation reactions such as by the use of potassium permanganate, aqueous nitric acid and the like oxidation agents.

PREFERRED EMBODIMENT 2,5-dichloroterephthalic acid, aqueous sodium hydroxide, and cuprous oxide are charged to a pressure autoclave fitted for mixing. The amounts of each component are proportioned to yield a reaction mixture having the relative molecular amounts of dichlor'oterephthalate salt, sodium hydroxide, water and copper catalyst of 1:13: 1 3 :0.l6, respectively. Under an atmosphere substantially free of oxygen (see U. S. Pat. No. 2,762,838) the autoclave plus charge in the liquid phase are heated at a temperature of 200210C. for about one hour. The resulting reaction mixture is then cooled and acidified by dissolving carbon dioxide gas in the mixture. The liberated hydroquinone is then removed by extraction with a suitable organic solvent, for example ethyl ether, and recovered by distillation.

The aqueous solution remaining after removal of the hydroquinone contains a minor amount of reaction intermediates, mainly monochlorohydroxybenzene carboxylates and sodium bicarbonate from the main reaction (two moles of sodium bicarbonate for each mol of hydroquinone produced) and from excess sodium hydroxide. This solution is regenerated for recycle to the process by the addition of calcium oxide and filtration to remove the insoluble calcium carbonate formed in the regeneration stage as well as some of the sodium chloride, i.e., that amount in excess of solubility. Afteradditions of the base and water to adjust for mechanical losses in the processing, the regenerated caustic medium is recycled to the process. The conversion of the feed is about -95 mol percent and the yield is 9 5-9 8 mol percent.

THE REACTION EQUATIONS The chemical conversions-effected in the process of the invention may be summarized as follows: C,H (CO,Na) Cl 4NaOH pCH,(ONa), 2NaCl ZNaHCO H 0 I Nal-ICO; NaOH Na,CO H 0 (2) pC,,I-l.,(ONa) +2CO 2H O pC H,(Ol-I), ZNaHCO;

Na CO (30 H O ZNaI-ICO, NaHCO, CaO NaOH CaCO I TEMPERATURE The instant process may be carried out over a range HYDROXIDE REACTANT in order to effect the displacement of chloride and carboxyl (decarboxylation) groups herein an exceptionally strong basic medium is required. The alkali metal hydroxides in general satisfy this need. In particular sodium, potassium and lithium hydroxides and mixtures thereof are useful. For reasons of cost sodium hydroxide is preferred.

For each mol of the dichloroterephthalate salt present in the reaction mixture (see equation 1 above), at least 4 mols of the alkali metal base is necessary for the satisfaction of the stoichiometric requirement. A substantial excess of the base should be present in order to reduce a polymer producing side reaction to a satisfactory level. For this purpose for each mol of salt feed at least 6 mols of base should be present. Best results in general obtain when the amount of the base is in the range 14-14 mols per mol of the dichloroterephthalate. Larger relative amounts, for example as much as 20 mols and more, may be employed.

ACIDIFICATION Acids in general having an acid strength greater than hydroquinone are suitable for the liberation of hydroquinone from its alkali metal salt. Mineral acids are satisfactory because of the low cost. However, carbon dioxide (carbonic acid) is preferred as an acidifier because its use permits regeneration of the excess alkali metal hydroxide and an easy control of pH in the range 6-7 (see reaction equations above). This pH is sufficient to free hydroquinone but does not liberate minor amounts of unconverted carboxylate salt feed or intermediates which may be present in the acidified reaction product mixture.

WATER DILUENT From an inspection of equation 1 above, water does not appear to be a reactant in the reaction system. However, in the absence of water the results are poor and the processing is difficult. Mixing and local overheating effects in particular are not good. At least about 0.5 mol of water per mol of hydroxide should be present in the mixture. An excess of water relative to the hydroxide, on the other hand, adversely affects the desired reaction. When the mol ratio of water to hydroxide exceeds about I to l, the results become progressively poorer as the ratio becomes larger. From this fact, it is inferred that amounts of water substantially in excess of a 1:1 ratio reduces the basicity of the hydroxide reagent. Useful results are achieved when the water to hydroxide ratio is below about 9, but for satisfactory conversions of the dichloroterephthalate salt to hydroquinone, this ratio should not exceed about 3-5; and, in general, for best results for each mol of hydroxide in the reaction mixture, the amount of water should be in the range 1 to 3 mols, preferably one mol of water.

Along with water, if desired, methanol and ethanol may be added to the reaction system as diluents. However, because of the relatively lower boiling points of these alcohols, their presence in the system results in higher system pressures. Similarly, dimethylsulfoxide may also be used as a diluent (see for example U. S. Pat. No. 3,481,991) for the present displacement reaction, but such use complicates the hydroquinone recovery stage and hence is not a preferred mode.

REACTION PROMOTERS Hydroquinonc is produced by the process herein in the absence of catalysts. The presence in the reaction medium of a copper compound, however, is beneficial. Copper compounds, in general, which convert to oxide(s) of copper in the presence of strong alkali metal hydroxides are useful promoters for the reaction. Thus representative promoters suitable for use herein include cuprous oxide, the copper chlorides, carboxylates, nitrates, sulfates, acetates, and the like copper compounds.

Trace amounts of copper oxide are beneficial. Satisfactory amounts are in the range 0.01 to 0.25 mol per mol of the dichloroterephthalate salt. Larger relative amounts may be used, but cost becomes a factor. The preferred range is 0.05 to 0.2 mols of promoter (based upon copper) per mol of the dichloroterephthalate feed.

The following examples are for the further illustration of the invention.

DICHLORO-P-XYLENE Example 1 p-Xylene was chlorinated by introducing chlorine gas into p-Xylene containing about 5 weight percent (based upon p-xylene) of ferric chloride while maintaining the reaction temperature at about 20C. After the addition of 1.8 equivalents of chlorine per mol of the xylene, the optimum yield, about 67 mol percent of dichloro-p-xylene, was produced. Separation and recovery of the dichloro derivative by distillation completed the preparation. The product was a mixture which was 65 percent 2,5-dichloro-p-xylene and the balance was a mixture of 2,3- and 2,6-dichoro-pxylene.

2,5-DlCHLOROTEREPHTl-IALIC ACID Example 2 2,5-dichloro-p-xylene 1,4-dichloro-3 ,6- dimethylbenzene) was oxidized in a liquid phase air oxidation employing acetic acid as the solvent and cobalt acetate as the catalyst. The reaction temperature -was in the range 1 l0-l20C. The resulting 2,5- dichloroterephthalic acid was recovered by conventional means, including filtration and recrystallization.

HYDROQUINONE Example 3 Sodium 2,5-dichloroterephthalate and sodium hydroxide in a mo] ratio of-l to 25, respectively, sufficient water to yield a hydrozide to water mol ratio of 1 to 2.6, respectively, and based upon the salt, 10 weight percent of cuprous oxide were charged to a shaking autoclave, filling about half of the reactor which was then sealed. The autoclave and its contents were maintained at about 200C. for about two hours. The product was worked up by conventional means, including acidification and extraction. The conversion of the salt was 65 mol percent, and the yield of hydroquinone was 76 mol percent.

The data in the above example clearly demonstrates that alkali metal salts of 2,5-dichloroterephthalic acid is effectively converted to hydroquinone by the novel process herein described.

It is to be understood that my invention is in no way limited by the specific examples given herein and that many modifications and variations may be made without departing from the spirit and scope of my inventive contribution as set forth in the following claims.

I claim:

1. The process for the production of hydroquinone which comprises reacting an alkali metal salt of 2,5- dichloroterephthalic acid with an alkali metal hydroxide by heating a mixture of the reactants in the liquid phase in the presence of water, wherein the heating is above about 150C. and below about 270C.; wherein for each mol of the salt, the mixture contains an amount of the hydroxide in the range from about 4 to 20 mols; and wherein for each mol of the hydroxide mixture contains an amount of water in the range from about 0.5 to 20 mols; and acidifying the resulting reaction mixture.

2. The process as in claim 1 further characterized in that the reaction is promoted by copper oxide and in that for each mol of the salt an amount of the copper oxide in the range from about 0.01 to 0.25 mol is present in the reaction mixture.

3. The process as in claim 1 further characterized in that the temperature is in the range from about 190C. to 210C., in that the amount of hydroxide is in the range from about 6 to [4 mols, and in that the amount of water is in the range from about 1 to 3 mols.

4. The process as in claim 3 further characterized in that the hydroxide is sodium hydroxide, in that the amount of the hydroxide is about 13 mols, in that the amount of water is one mol per mol of hydroxide, and in that the reaction is promoted by the presence in the mixture of about 0.16 mol of cuprous oxide per mol of the salt.

5. The process as in claim 1 further characterized in that carbon dioxide is used for the acidification.

6. The process for the production of hydroquinone which comprises reacting the sodium salt of 2,5- dichloroterephthalic acid with sodium hydroxide by heating a mixture of the reactants, water, and copper oxide in the liquid phase at a temperature of about 200212C. for a period of about one hour, said mixture containing for each mol of the salt about 25 mols of the hydroxide, about 66 mol of water and about 0.16 mol of the oxide, and acidifying the resulting reaction product mixture.

7. The process as in claim 6 further characterized in that hydroquinone is recovered from the resulting aqueous reaction mixture by:

a. Acidifying the mixture with carbon dioxide; and

b. Separating the hydroquinone from the acidified mixture by extraction with ether.

8. The process as in claim 7 further characterized in that the aqueous residue remaining after the extraction is treated with calcium oxide, filtered, and used in a succeeding process cycle.

9. The process of claim 2 further characterized in that the copper oxide promoter is produced in situ. 

2. The process as in claim 1 further characterized in that the reaction is promoted by copper oxide and in that for each mol of the salt an amount of the copper oxide in the range from about 0.01 to 0.25 mol is present in the reaction mixture.
 3. The process as in claim 1 further characterized in that the temperature is in the range from about 190*C. to 210*C., in that the amount of hydroxide is in the range from about 6 to 14 mols, and in that the amount of water is in the range from about 1 to 3 mols.
 4. The process as in claim 3 further characterized in that the hydroxide is sodium hydroxide, in that the amount of the hydroxide is about 13 mols, in that the amount of water is one mol per mol of hydroxide, and in that the reaction is promoted by the presence in the mixture of about 0.16 mol of cuprous oxide per mol of the salt.
 5. The prOcess as in claim 1 further characterized in that carbon dioxide is used for the acidification.
 6. The process for the production of hydroquinone which comprises reacting the sodium salt of 2,5-dichloroterephthalic acid with sodium hydroxide by heating a mixture of the reactants, water, and copper oxide in the liquid phase at a temperature of about 200*-212*C. for a period of about one hour, said mixture containing for each mol of the salt about 25 mols of the hydroxide, about 66 mol of water and about 0.16 mol of the oxide, and acidifying the resulting reaction product mixture.
 7. The process as in claim 6 further characterized in that hydroquinone is recovered from the resulting aqueous reaction mixture by: a. Acidifying the mixture with carbon dioxide; and b. Separating the hydroquinone from the acidified mixture by extraction with ether.
 8. The process as in claim 7 further characterized in that the aqueous residue remaining after the extraction is treated with calcium oxide, filtered, and used in a succeeding process cycle.
 9. The process of claim 2 further characterized in that the copper oxide promoter is produced in situ. 